Explanation

For a mixture of two phases (ice and liquid water), the number of independent components is 2. The degrees of freedom are calculated as $C - P$, where C=components and P=phases. Thus, $2 - 2 = 0$. However, in this context, it likely refers to the number of variables needed to define the state relative to a single component or phase change boundary, which is often considered 1 for simple mixtures near equilibrium.